The present invention relates to an agitator-type ball mill. More particularly, it relates to an agitator-type ball mill which has a working or milling chamber bounded by a wall having an inner jacket, an outer jacket, and a helical passage for receiving a cooling or heating medium formed between the jackets.
Agitator-type ball mills of the above-mentioned general type are known in the art. One jacket of a known mill is provided with a helical groove in which a band laterally bounding the passage between the jackets is inserted. One such construction is disclosed in the German Offenlegungsschrift No. 2,634,835. The agitator-type ball mill has a working or milling chamber with a wall formed by a metallic inner jacket and a metallic outer jacket. Both jackets are welded at both ends to a flange. An intermediate space is provided between the jackets, and a helical groove of a rectangular cross section is formed on the outer surface of the inner jacket. A band havinng a rectangular cross section and constituted of metal is inserted in the groove. The ends of the band are welded to the inner jacket. The outer rectangular portion of the band abuts against the outer jacket so that a helical passage for receiving a cooling or heating medium is formed between the jackets and the band. The band has a width, measured in the axial direction of the working chamber, which is substantially equal to the radial dimension of the intermediate space between the jackets. Thereby, the band, after its insertion into the intermediate passage, is practically completely rigid.
Town water is generally utilized as a cooling or heating medium during the operation of the agitator-type ball mill. Since this water generally contains impurities, minerals, and dissolved salt, deposits, particularly of lime, are formed in the passage between the jackets, and the band. These deposits can clog the passage so that is can no longer perform its intended functions. Since both jackets are fixedly welded with one another, it is generally impossible to clean the passage without destruction of the chamber wall. Thereby, when the helical passage is clogged, the entire wall of the mill must be exchanged.
The above-mentioned German Offenlegungschrift also described an example in which both jackets are releasably connected with one another. The lateral limiting of the passage for the cooling medium is, however, attained not by a band insertable in a groove of a jacket, but by a rib of the inner or outer jacket. It has been shown, that even though the both jackets are releasably connected with one another, the clogging of the passage makes impossible separation of the inner and outer jackets from one another in the known agitator-type ball mills without destruction. The deposits which take place in the passage connect the rib provided on the one jacket, with the other jacket so firmly that separation of the jackets is no longer possible.